Process for the preparation of talking machine plates



Patented June 11, 1935 PROCESS TALKING MACHINE PLATES Alfred Otto Thomae, Berlin-Steglitz, Germany No Drawing. Application January 10, 1930, Serial No. 420,023. In Germany January 11, 1929 r 2 Claims.

My invention relates to a process for the preparation of talking machine plates, which by removing noise permit a lasting use. The process consists therein, that gelatinized acetyl cellulose with camphor or camphor substitute is used as material from which the plates are to be made.

In order to attain certain .qualities, such materialmust be dried at a certain temperature and for a certain period, and it has proved advisable to lengthen the drying time in accordance with the thickness of the plate to be 'made, so that for each mm. thickness of the plate a drying time of twenty-four hours of the material is reckoned. Usually a thickness of 0.5 mm. is sumcient, the drying time lasts for approximately one hundred and twenty hours. i

The temperature at which such drying is car,- ried out, is between 40 and 80.

For the preparation of the record plate itself from such previously dried material a pressure of 200 atmospheres and over must be employed and the pressing is advantageously undertaken when the record plate is heated, the temperature varying between and 90.

Gelatinized acetyl cellulose or similar substances with camphor or camphor substitute materials must be made soft by heat or dissolved in suitable solvents, as, for example, acetone. The

invention further extends to the special methods of preparation of such substances, used for the preparation of talking machine plates, asare soluble or rendered fluid by heat. As it has been proved, that during pressing of such plates by means of compressed air unevenness and unequal pressure can easily occur, the dissolved or fluid-rendered mass is, according to theinvention sprayed on to the plates provided with sound waves or figures. The spraying is effected advantageously in a very finely divided condition, so that a very fine layer-is deposited all over the matrix plate, completely filling up the finest parts, so that the plate produces throughout a true and complete picture of the matrix. To this layer which hasbeen sprayed on or laid on with a brush, any kind of strengthening material can then be applied, or the whole plate can be prepared complete from the. uniformsubstance. to

The use of acetyl cellulose gelatinized with camphor or camphor substitute materials for the production of records has the special advantage that disturbing noises are eliminated. The present invention relates to a practical method of manufacture, because the qualities of the raw materials vary often widely. It has been necessary to test each new shipment of the raw materials in the manufacture of sound records in order to find the pressing temperature most suitable for the shipment. This vague testing is made unnecessary by the invention.

The drying temperatures must lie between 40 and 80, and these temperatures, or temperature rangesrespectively, must thereforebe considered as critical beginning and end temperatures. p

The plates of raw material are therefore dried at a temperature between 40 and 80 in conformity with the qualities of these plates of raw material, which require a temperature between 40 and 80.

According to the invention the manufacturer of the plates of raw material informs the manufacturer of the records that the shipment of the plate strips has been dried at 60 and the record manufacturer knows then that he must use a pressing temperature of for the strips of raw material dried at a temperature of 60.

If, for instance, the following drying temperatures ofthe plates of raw material are assumed: 40, 44, 48, 52, 60, 68, 76, the corresponding pressing temperatures for the records are: 60, 63, 66, 69, 75, 81, 87 and 90.

The invention incorporates therefore the following three ideas or principles: r 1. A drying period of 24 hours for each 0.1 mm. thickness of the plates in the production of the plates of raw material. t

2. The critical temperature ranges for the drying of the raw material strips lie between 40 and 80.

3. The critical temperatures for the pressing of the plates lie between the corresponding range of 60-90". r

Two separate plates prepared by spraying can be made into a single uniform plate to form a doublesided record by sticking together the sides which are not provided with sound waves or joining them together in any other suitable manner. Instead of gelatinized acetyl cellulose with camphor or camphor substitute materials other sub,- 7 stances can be used, which have the same quali I ties such as acetyl cellulose with camphor, cam 50 phor substitute materials is known in commerce under the names Siccoid or Rhodoid.

The plates made of such an artificial substance are flexible, and unbreakable, water-benzine-oil proof and non-inflammable.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that What I claim is:

1. The method of producing sound records from gelatinized acetyl cellulose, consisting in drying such material at a temperature of from C. to 80 C. for a period of substantially 24 hours for each one-tenth millimeter thickness of the record disc to be made therefrom, forming a record from such dried material in a heated press the temperature of which is from C. to90 C. and

during such forming subjecting such record to a pressure of substantially 200 atmospheres.

2. The method of producing sound records from gelatinized acetyl cellulose, consisting in drying the acetyl cellulose at a temperature of from 40 C. to C. for a period of substantially 24 hours for each one-tenth millimeter thickness and pressing such dried acetyl cellulose in a heated press the temperature of which is from 60 C. to

C. and at a pressure of substantially 200 at- 10 mospheres.

ALFRED OTTO THOMAE. 

